1. Field of the Invention
The present invention relates to an inner mold for molding a cylinder, which inner mold has a bore-forming core for forming a cylinder bore and a shell core disposed in fitting engagement with holes formed in the bore-forming core for forming a recess in the cylinder wall such as scavenging passages.
2. Description of the Prior Art
A type of inner mold has been used in molding, for instance, a cylinder of an air-cooled 2-cycle internal combustion engine which has two scavenging passages. However, the arrangement of a conventional inner mold of this type, described in detail later with reference to a drawing, has the following disadvantages. That is, when the molding has been completed and when it is necessary to remove projections of the shell core where the shell core has been kept in fitting engagement with the bore-forming core and which remain within rectangular holes of the bore-forming core after the bore-forming core and the other portion of the shell core have been pulled out from the cylinder, the operator has to manually crush the remaining projections of the shell core into pieces, and these crushed pieces of the shell core have to be blown off by, for example, air under high pressure. Thus, this operation of removing the remaining portions of the shell core from the bore-forming core requires a time-consuming manual operation, thereby leading to the problem that the automatization of cylinder molding may be hindered, as well as the fact that the mold sand may scatter and polute the surroundings.